:) Cái này tìm Max chứ

Xét mẫu : x²+2x+15=x²+x+x+1+14=x(x+1)+(x+1)+14=(x+1)(x+1)+14=(x+1)²+14.

Ta có : (x+1)²\(\ge0\) với mọi x

=> (x+1)²+14\(\ge14\) với mọi x

=> Q \(\le\dfrac{12}{14}=\dfrac{6}{7}\)

Dấu "=" xảy ra <=> (x+1)²=0

=> x+1=0

=> x=-1

Vậy Max Q = \(\dfrac{6}{7}\Leftrightarrow x=-1\)

Có khi hạng 2 là 1 khuyết điểm

a) 3-x+2x+7=2x

=> 3+x+7=2x

=> 10+x=2x

=> x-2x=-10

=> -x=-10

=> x=10

Vậy x= 10

b) 3(x+1)=2

=> x+1=2/3

=>x=2/3-1

=> x= 2/3 - 3/3

=> x= -1/3

Vậy x = -1/3

1. This is the beast computer I have ever used .

-> I have never had a computer better than this one before .

2. He hasn't chatted with his classmates through the internet for ages.

-> It's ages since he last chatted with his classmates through the internet

3. Trung's parents gave him a micro computer on his birthday.

-> Trung was given a micro computer by his parents on his birthday .

4. He has never played a computer game before.

-> this is the first time that he has played a computer game

5. We haven't seen her since we left university.

-> the last time we saw her was ...( chịu)

II. Change into passive form .

1.People throw away billions of cans every year all over the world.

-> Billions of cans are thrown away every year all over the world

3. Who usually writes letters ?

-> Are letters usually written ?

6. My classmate , Minh plays football beautifully.

-> Footbal is played beautifullly by Minh , my classmate.

9. I won't give him his book

-> He won't be given his book by me

10. Somebody cleans this room every day

=> This room is cleaned everyday .